(The Washington Post) – With President Trump’s decision on U.S. participation in the Paris climate accords expected in the next few days, there has been widespread discussion of the many consequences that climate change will have for us and our children, including extreme weather events, displacement of people, submergence of lands and devastation to our oceans. But one of the most potentially deadly effects has been far less discussed: an increase in the spread of dangerous epidemics and the risk of a global pandemic.

As the Earth’s climate alters, we are seeing changes in where and how humans live; these changes increase the risk that deadly diseases will emerge and spread more rapidly. While the interactions between climate change and disease are hard to predict with certainty, the scientific linkages are unmistakable. If we fail to integrate planning for the impact of climate change with planning for the prevention and management of pandemic disease, the consequences will be deadly.

The link between climate and disease is most often identified through the spread of disease vectors such as mosquitoes. As areas warm, habitats for insects — mosquitoes and deer ticks, for example — expand, exposing new populations to new disease threats. As Maryn McKenna recently explained in the New York Times Magazine, the approximately one degree Celsius increase in average temperatures the planet has experienced is “changing the numbers and distribution of the insect intermediaries that carry diseases to people.” Most immediately, we could see a larger number of people at risk in the United States from Zika this summer as the Aedes aegypti mosquito moves farther north, complicating the already challenging efforts to constrain the disease.

But a second, and less appreciated, interaction between climate change and epidemics occurs when humans and animals are forced to compete for dwindling habitat and resources. The scenario behind Ebola’s rise and global threat in 2014 illustrates this point. Climate change destroys habitats and stresses animal populations such as the bats of West Africa, forcing them to hunt for food nearer to humans. Humans, likewise pressed by climate impacts, encroach more closely on animal habitats. While we cannot know that climate change was the cause of the specific interaction between bats and humans that is believed to have launched the Ebola outbreak in Guinea, we will see more of these interactions in the future, and more epidemics as a result.

Ebola demonstrates that even localized dislocation of people and animals can create global risk. Climate change is a threat multiplier for much broader dislocation — accelerating the complex factors that drive people from their homes. While in some cases climate-affected dislocation will be “planned” — as with the climate refugees in Louisiana or on remote Pacific islands such as Kiribati — more often it will occur in large, unplanned migrations that amplify regional instability and crisis. This dynamic can also drive migrations from rural into urban areas, as occurred in Syria, where the 2006-2010 drought killed off 80 percent of the country’s livestock and helped drive more than 1.5 million people into stressed urban centers. The U.S. intelligence community’s bottom-line assessment of the risk is plain: “Over 20 years, the net effects of climate change on the patterns of global human movement and statelessness could be dramatic, perhaps unprecedented.”

We saw Ebola breach the rural-to-urban interface in West Africa; the outcome and extent of the current outbreak of Ebola in Congo remains to be seen. As climate change accelerates the movement of people, the risks of disease formation and transmission will multiply. [more]